Integrated circuits ("ICs") have evolved greatly over the years. When first introduced, ICs contained only a few circuit elements. Presently, a complex IC may include millions of circuit elements. Thus, ICs have become increasingly complex and valuable over the years. Because of the value of the ICs, theft in the industry has increased greatly and a black market has developed in which stolen parts are trafficked. Because individual identification of parts helps to curb theft of the ICs, techniques for individually identifying ICs have been developed.
Previous techniques for identifying ICs to prevent theft included labeling the IC package. Unfortunately, the labeling could be easily removed and provided only minimal protection. Labeling the substrates of the ICs, while providing a more suitable means for identification, required numerous mask sets for functionally equivalent parts and was too expensive to justify the benefit.
Prevention of theft, however, is not the only reason to individually identify ICs. In many applications, ICs must be electrically identified so that they are uniquely addressable. Cellular telephone systems, for example, require that each individual phone on the system responds only to signals directed to it. Thus, in a typical cellular phone system, an IC in each cellular phone is programmed with a unique identification code so that the phone is electrically identified. Based on this identification code, the cellular telephone system accesses the phone individually by including the phone's identification code in a transmitted signal. The phone recognizes the identification code, enables signal receipt circuitry, and then receives the signal. Because each phone on the cellular system has a unique identification code, the cellular telephone system may address each phone separately by selectively transmitting identification codes.
Identification devices commonly used to identify ICs employ non-volatile memory chips such as electronically programmable read-only-memory (EPROM) and electronically erasable programmable read-only-memory (EEPROM) chips, these chips being written with a unique identification code. Because these components provide non-volatile memory, once the identification code is written into them, it remains indefinitely and may be read from the memory chips as needed to use in a decoding function. The identification code may also serve to identify the individual IC if stolen.
EPROMs and EEPROMs do have limitations, however. In certain environmental conditions, their memory contents may be inadvertently destroyed. Also, because they may be written more than once, the contents may be intentionally altered if stolen. Once rewritten, the identification code is lost. Thus, EPROMs and EEPROMs provide little protection to prevent theft and only adequate performance in addressing functions.
Therefore, a need exists for an integrated circuit identification apparatus and method that is non-volatile, that may not be altered once it has been programmed, and that is inexpensive to implement.